HVAC system with electronically controlled expansion valve

A method for controlling the release of refrigerant from an electronically controlled expansion valve, the method comprising:

• determining an airflow percentage for the operation of a fan, the airflow percentage corresponding to a quantity or rate of flow of air to a heat exchanger;
• determining an estimated pressure drop across the heat exchanger using a direct correlation which is stored in a memory of a controller where the direct correlation is between airflow percentage and estimated pressure drop across the heat exchanger and where airflow percentage is used as input to the direct correlation and estimated pressure drop is an output from the direct correlation;
• determining an outlet pressure for refrigerant exhausted from the heat exchanger based on an inlet pressure of refrigerant at an inlet of the heat exchanger and the estimated pressure drop;
• determining, using at least the outlet pressure, a heat exchanger exit saturation temperature;
• sensing, by an outlet temperature sensor, an outlet temperature for refrigerant exhausted from the heat exchanger;
• deriving, from a comparison of the sensed outlet temperature and the heat exchanger exit saturation temperature, an estimated superheat value;
• and
• adjusting a flow of refrigerant released by the electronically controlled expansion valve based on an outcome of the comparison between the derived estimated superheat value and the reference superheat value.

A method for controlling the release of refrigerant from an electronically controlled expansion valve, the method comprising:

• determining, by at least one controller, an airflow percentage for a flow of air by a fan to an evaporator;
• determining an outlet pressure of refrigerant exhausted from the evaporator using (1) an inlet pressure of refrigerant to the evaporator, and (2) the determined airflow percentage and a computational relationship stored in a memory of the at least one controller between airflow percentage and an estimated refrigerant pressure drop across the evaporator where airflow percentage is used as input to the computational relationship and estimated refrigerant pressure drop is an output from the computational relationship;
• determining a saturated temperature for refrigerant exhausted from the evaporator using at least the estimated refrigerant pressure drop across the evaporator;
• sensing, by a temperature sensor, an outlet temperature of refrigerant exhausted from the evaporator;
• comparing the saturated temperature and the sensed outlet temperature of refrigerant to determine an estimated superheat value;
• comparing the estimated superheat value to a reference superheat value;
• and
• adjusting the release of refrigerant from the electronically controlled expansion valve based on the outcome of the comparison between the estimated superheat value and the reference superheat value.